A technique is known that obtains various types of information on a quantity of heat during the combustion in an internal combustion engine as disclosed, for example, in JP-A-2006-144643. Specifically, the above-referenced publication discloses a technique that uses an output value from an in-cylinder pressure sensor to calculate a calorific value immediately after the completion of combustion and calculates a combustion air-fuel ratio based on the calorific value thereby obtained.